The invention relates to a sputtering cathode on the magnetron principle, having a target consisting of at least one piece of the material to be sputtered and having a system of magnet units of alternately different polarity disposed behind the target, by which at least one continuous magnetic tunnel of arcuately curved lines of force is formed, and the magnetic unit poles facing away from the target are joined together by a yoke of soft magnetic material.
German Federal Republic OS No. 34 42 206 (U.S. Pat. No. 4,601,806) discloses a sputtering cathode of the kind described above, which is designed for sputtering targets of ferromagnetic materials. In one of the two embodiments, two magnet units lying concentrically one inside the other form, in conjunction with two concentric air gaps disposed in the target, two endless magnetic tunnels, one inside the other, of arcuately curved lines of force. Since, however, in this case the magnetic fields are magnetically in series with one another across the two air gaps, the field strengths of the two tunnels cannot be controlled independently of one another. Thus, in the area of the two magnetic tunnels, different sputtering rates develop, and in the area of the substrate facing the target greatly different rates of deposition, so that the coating thickness is very irregular.
In the case of bar cathodes German Federal Republic OS No. 22 43 708 discloses the disposal of magnet units axially in tandem in order thereby to make the sputtering of the target material more even. For the planar targets therein described it is also stated that concentric magnetic tunnels situated one inside the other can be provided. In this case too, no possibilities are provided for any separate adjustment of each magnetic tunnel independently of the adjacent tunnel, nor is such adjustment possible.
It is known through a sputtering cathode of the kind described above which is sold under the name "Con Mag" by the Varian company to provide within and at a distance from a circular yoke plate a circular disk-shaped yoke plate, and to associate with each yoke plate two magnet units of opposite polarity acting independently of one another, while a target having a conical sputtering surface is disposed over the circular ring-shaped magnet system and a planar target plate is disposed over the circular disk-shaped magnet system. Means for controlling independently of one another the magnetic field strength of the two tunnels formed are not provided. In this sputtering cathode the sputtering effect must be accepted as determined by the position of the magnetic tunnels relative to the sputtering surfaces.
Now, especially when the target consists of a nonferromagnetic material, the distance of the magnet system or systems from the target has a considerable influence on the distribution of the lines of force over the sputtering surface and hence on the so-called "erosion profile." To compensate the increasing consumption of the target material by the formation of an erosion pit, German Federal Republic OS No. 30 47 113 (U.S. Pat. No. 4,426,264) discloses varying the distance between the magnet system and the back of the target with the advancing consumption of the target material. The magnet system in question, however, consists of only two magnet units which produce a single magnetic tunnel.
Now, the invention is addressed to the problem of devising a sputtering cathode both for magnetic and for nonmagnetic target materials which will result in coatings of very uniform thickness and permit an especially good utilization of the target.